Nonvolatile memories retain the data stored in them even when the power has been removed. Such are particularly needed in digital cameras, smartphones, radio frequency identification (RFID) tags, and other applications. One commonly available type of nonvolatile memory is the programmable read-only memory (“PROM”), which uses wordline-bitline crosspoints. These may include fuses, antifuses, and trapped charge devices (for example, floating gate avalanche injection metal oxide semiconductor (“FAMOS”) transistor) to store logical information. The term “crosspoint” refers to the intersection of a bitline and a word line.
An example of one type of PROM cell that uses the breakdown of a silicon dioxide layer in a capacitor to store digital data is disclosed in U.S. Pat. No. 6,215,140, to Reisinger, et al., which is herein incorporated by reference in its entirety. The basic PROM disclosed by Reisinger, et al., uses a series combination of an oxide capacitor and a junction diode as the crosspoint. An intact capacitor represents the logic value 0, and an electrically broken-down capacitor represents the logic value 1. The thickness of the silicon dioxide layer is adjusted to obtain the desired operation specifications. Such cells are described in U.S. Pat. Nos. 6,667,902; 6,700,151; 6,798,693; and 6,650,143 all to Jack Z. Peng. All of which are incorporated by reference herein in their entireties. Improvements in the various processes used for fabricating the different types of nonvolatile memory tend to lag improvements in widely used processes such as the advanced CMOS logic process as disclosed in United States Published Patent Application 2010/0091545 to Jack Z. Peng, et al., which is incorporated herein by reference in its entirety.
XPM™ is a proprietary antifuse-based, embedded non-volatile memory (NVM) marketed by Kilopass Technology, Inc., (Santa Clara, Calif.) as an electrical programmable fuse (eFUSE) replacement. XPM is a field programmable memory that can provide higher security, larger capacity, smaller footprints, and lower active and standby power demands. XPM™ is a foundry agnostic, and its associated IP can be well protected and transferred between silicon foundries.
Prior art NVM cells, e.g., as described in U.S. Pat. Nos. 6,667,902; 6,700,151; 6,798,693; and 6,650,143 all issued to Jack Z. Peng, can require too much power for programming and for reading in particular applications. For example, conventional cells can require a programmed gate oxide (in a gate capacitor) to be pushed into its hard breakdown regions so a low enough resistance will result for a reasonable cell read sense current (1-10 μA). Conventional cells can also require a very high read voltage (Vwp), >2.5-3.3V. A large enough voltage drop is needed over the high resistance of breakdown gate oxide, e.g., 1-10 μA×500K ohms=0.5-5V. A resistance of 3M ohms will cause a drop of 3-10V. Some high resistance cells may not be read out with high enough signal levels. These examples indicate several disadvantages with the prior art memory technologies.
There is a need for NVM cells with improved performance and that overcome the shortcomings of the prior art.